1. Field of the Art
This invention relates to a catalyst for olefin polymerization. More particularly, this invention relates to a catalyst which, when used for polymerization of olefins, especially .alpha.-olefins having 3 or more carbon atoms, makes it possible to produce polymers of high stereoregularity under stable polymerization conditions advantageously from the viewpoint of commercial production.
2. Background Art
Conventional catalysts for olefin polymerization comprising a solid catalyst component, which consists essentially of titanium, magnesium and a halogen, and an organoaluminum compound have a high catalytic activity. When using such catalysts, however, it is necessary to further use electron donative compounds during polymerization when polymer products are required to possess high stereoregularity. The use of an electron donative compound as a third component (outside electron donor) usually entails lowering of polymerization rate due to occurrence of a reaction between the electron donative compound and an organoaluminum compound. In this case, an attempt to enhance polymerization rate for an improved productivity by elevating polymerization temperature is not successful since the rise of temperature promotes the above mentioned reaction. Moreover, the reaction will lead to difficulty in controlling the properties of a polymer product including its molecular weight.
Thus, there has been a search for development of catalysts which eliminate the above described problems and can ensure production of polymers having high stereoregularity in an increased catalytic yield without using an electron donative compound as a third component (outside electron donor).
Japanese Patent Laid-Open Pub. No. 138715/1983 discloses a polymerization process using a catalyst which does not comprise an outside electron donor and is formed from a solid component and an organoaluminum compound, said solid component being obtained by reacting (1) a titanium complex comprising tetravalent titanium, magnesium, a halogen and, as an essential constituent, an electron donor with (2) an organosilicon compound having Si-O-C bond in the co-presence of an organoaluminum compound or by treating the titanium complex with an organoaluminum compound and then reacting the thus treated titanium complex with the organosilicon compound.
This process, however, contributes toward eliminating the problems mentioned above but leaves much to be desired, for example, limitations of the performance of the product polymer obtained, the deterioration of the catalyst with an elapse of time, and a limited range of ratios between the quantities of the titanium component and the organoaluminum compound used during polymerization.